Rollers are frequently used in conveyors, packaging machinery, treadmills, and linear motion material handling devices. Rollers are typically mounted on fixed centers between parallel frames which provide adequate support for the rollers and the articles transported by the rollers. Various methods exist for mounting the rollers in the support frames. One of the most common methods is to use a roller having a spring-loaded shaft. The shaft is extended on both ends of the roller. To install the roller, the shaft is moved axially against the force of the spring and "snaps" in place between the parallel frame members into a suitable hole or slot.
In order to prevent rotation of the shaft in the frame, which could result in substantial wear, the roller shaft and the mating mounting holes or slots in the frame have a polygonal configuration to prevent rotation. For example, the shaft and the mating mounting holes could be hexagonal in shape. Alternatively, when round shafts are used, one or more flats may be formed on the shaft to prevent rotation of the shaft in the frame.
In order to accommodate the tilt angle required to install a spring loaded roller into mounting holes, the mounting holes in the frame are generally 0.030 inches to 0.068 inches oversized to facilitate assembly. Alternatively, if mounting slots are used, the width of the slots are similarly oversized. In most applications, the resulting "play" between the shaft and the mounting hole in the frame presents no operating difficulties. However, in powered conveyors where vibration and side movement can occur, there is a tendency for the shaft to vibrate in the mounting hole causing wear and creating excessive noise. If the mounting hole in the frame wears excessively, it is possible that the shaft will start to rotate in its mounting hole. This unintended rotation of the shaft may lead to premature failure of the roller and/or shaft as well as the frame.
In powered conveyors, the shaft wear problem is exacerbated when the rollers rotate at high speed. Most conveyor rollers utilize welded-steel tubing. Differences in wall thickness of the tube around its circumference as well as a weld seam inside the tube may result in roller tube imbalance. This roller tube imbalance is not a problem in slow speed applications. However, at high speeds, the dynamic imbalance of the tube causes the roller and the shaft to oscillate in the frame mounting hole causing noise and accelerating wear.
Accordingly, there is a need for a roller mounting method which eliminates the play between the roller shaft and the mounting holes in the frame so that excessive wear is prevented.